It is known that by processing a silver halide photographic material finely divided metallic silver, so-called silver deposit, is formed in the developer (ref. e.g. Photographic Silver Halide Diffusion Processes by A. Rott and E. Weyde--The Focal Press, (1972), p. 67). The formation of silver deposit is particularly disturbing in automatic processing apparatus wherein it results in deposits of black silver on conveyor and transport rollers and smudging of photographic material conducted therewith.
The formation of silver deposit can be attributed to the presence in conventional developers of silver halide complexing agents like, e.g., sulphite and thiocyanate ions, which make silver ions still more soluble. In this medium the complex ions formed are effectively reduced to metallic silver nuclei. Growth of said nearly invisible fine nuclei leads to the formation of said silver deposit.
It is clear that more soluble silver halide grains, especially grains rich in chloride and/or fine grains, coated in one or more hydrophilic layers of a silver halide photographic material, are promoting the formation of silver deposit, although otherwise their higher development and fixing rates are highly appreciated. Moreover not only fine regular or globular grains, having a small average crystal size diameter of about 0.25 .mu.m or less are promoting the said formation, but also thin tabular grains having a grain thickness of less than about 0.2 .mu.m.
The silver halide emulsions utilized in high-contrast room-light-handleable elements are slow speed emulsions. The desired slow speed is achieved by the use of small grain sizes and by the doping of the silver halide grains with appropriate doping agents that control photographic speed.
In order to prevent the formation of silver deposit it has been proposed to add particular compounds to the developer, forming sparingly soluble and non-reducible silver salts, as, e.g., 5,5'-bis-1,2,4-triazolin-3-thiones or derivatives of 1,3,4-thiadiazole-2-thiols as described, e.g. in BE-P 606,550 and GB-P 1,120,963, 2-mercapto-1,3,4-thiadiazoles described in U.S. Pat. No. 3,212,892. A great variety of other mercapto compounds has been described in FR-P 1,470,235 and 1-phenyl-5-mercapto-tetrazole compounds having a --NHX substituent on the phenyl nucleus have been disclosed in GB-P 1,471,554. In the latter document it has been described that the emulsion layer may contain auxiliary coating agents such as saponin, sodium lauryl sulphate, dodecylphenol polyethylene oxide ether and hexadecyltrimethyl ammonium bromide.
The same result can be obtained by the presence in the developer of 1-phenyl-5-mercaptotetrazole, but if it is used in an amount higher than necessary for reducing fog in the silver halide photographic material, the sensitivity of the said material is markedly reduced. Such effect is probably due to the penetrating of the 1-phenyl-5-mercaptotetrazole from the developer liquid into the exposed photographic silver halide emulsion layer and its interaction with latent image nuclei. More recently triazolium thiolates for use in the developer have been described in, e.g., EP-A 0 533 182.
In EP-Specification 0 223 883 a method has been described which comprises the treating of a silver halide photographic material with an aqueous alkaline liquid in the presence of (i) a developing agent, (ii) a heterocyclic mercapto compound including an aliphatic group of at least 3 carbon atoms and (iii) a surface active agent, characterized in that said surface active agent is an anionic alkylphenoxy polyalkyleneoxy phosphate ester surfactant.
In EP-A 0 620 484, reduction of the so-called "pi-line" defect, especially for processed materials for non-destructive testing purposes, has been described. Such materials should comprise at least one vinyl sulphone compound as a hardening agent and at least one polyoxyalkylene compound as a surfactant in at least one of its hydrophilic layers. Combined with a processing method comprising a developing step wherein the developer comprises as a surfactant at least one anionic alkylphenoxy and/or alkoxy polyalkyleneoxy phosphate ester, sulphate ester, alkyl carboxylic, sulphonic or phosphonic acid and/or a salt thereof a remarkable improvement has been obtained. A similar result has been obtained as disclosed in EP-A's 0 621 506 and 0 620 483.
Although said methods are very effective it is not more than a "treating method" wherein the amount of silver nuclei is not decreased but wherein said nuclei are more "dispersed" and are merely inhibited to grow further to form larger crystalline silver deposits. No "curing" effect in the sense of reducing the generation of nuclei can be obtained with this method. Moreover the stability of the developer, especially its sensitivity to oxidation by contact with air oxygen, is not reduced either.
As silver chloride is the more soluble silver halide salt, and therefor especially suitable in rapid processing applications, the problem of sludge formation by processing light-sensitive silver halide materials comprising such grains is more pronounced.
Otherwise during the last years there is an enhanced interest in the use of thin tabular grains rich in chloride, said grains having [111] or [100] major crystal faces. Especially for thin tabular grains rich in chloride, having [100] major faces, the stability of the crystal habit is a highly appreciated additional advantage.
It is generally known that the said thin tabular grains with their large surfaces are desired, e.g., as they allow the adsorption of high amounts of spectral sensitizer(s), leading to strong absorption of incident radiation. As a result a high sensitivity can be expected. Furthermore, as scattering of incident radiation throughout parallel twin planes is reduced, sharpness of the processed material is expected to be better. And last but not least the covering power of thin tabular grains comprised in coated layers of forehardened materials is not reduced in the processing of the said materials.